1. Field of the Invention
The present invention relates to a device for detecting an abnormal condition of an actuator or a sensor. More specifically, the invention pertains to a device for regulating an air intake into an internal combustion engine, a device for controlling an amount of fuel injection in the internal combustion engine, and respective methods.
2. Description of the Related Art
In an internal combustion engine, a throttle valve is generally installed in an air intake conduit for adjusting an air intake and driven by accelerator with wire link. A structure which the throttle valve is driven by an actuator like a motor is proposed recently as a linkless throttle valve. For the improved reliability, such a structure preferably includes a mechanism for pressing a throttle valve in a fail-safe direction under an abnormal condition of a driving system or a device for detecting abnormality of an actuator. In description of the specification, the actuator represents a whole system for driving a throttle valve including a driving source such as a motor and a power transmission mechanism.
A prior art structure is described according to an exemplified link-less throttle where a throttle valve for controlling an air intake in an internal combustion engine by a stepping motor (actuator). FIG. 1 schematically shows an electronically controlled throttle for controlling an opening of a throttle valve TV disposed in an air intake system of an internal combustion engine by means of an actuator. A first electronic control unit EC1 detects a driver's operation of an accelerator AC with a sensor, determines a target opening .alpha. of the throttle valve TV based on a variety of data including a rotation speed of the internal combustion engine and a vehicle speed, detects an actual opening .theta. of the throttle valve TV with a throttle opening sensor SS, and drives the actuator AA to make the actual opening .theta. of the throttle valve TV equal to the target opening .alpha.. Such an electronically controlled throttle is generally used for restricting an output of the internal combustion engine and attaining a linearity of an operation of the accelerator to an output of the internal combustion engine.
In this conventional system, an amount of fuel injection in an internal combustion engine is determined by a second electronic control unit EC2 for electrically opening and closing a fuel injection valve. The amount of fuel injection is determined according to operating conditions of the internal combustion engine, more specifically to an air intake into the internal combustion engine.
In these electronically controlled throttles, abnormality in the actuator directly causes abnormality in the opening of the throttle valve or the output of the internal combustion engine. It is thus essential to detect such abnormality without delay. The throttle valve is generally pressed in a full-closing direction by means of a spring to be controlled for ensuring safety under an abnormal condition of the actuator. A prior art device detects a rotation speed of a throttle valve and determines that the throttle valve is forcibly rotated by means of a spring or the like to cause abnormality such as step-out of a stepping motor when the rotation speed exceeds an upper limit of a driving speed of the throttle valve by an actuator as disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 62-93442 `CONTROL DEVICE FOR OPENING AND CLOSING THROTTLE VALVE`.
Such a conventional throttle valve control device is only directed to a single throttle valve structure and not applicable to a dual throttle valve structure. A conventional system can not be applied to the dual throttle valve structure where a second throttle valve is disposed in series with a first throttle valve directly driven by an accelerator since the second throttle valve is generally pressed in a full-opening direction and an air intake is substantially not affected by the movement of the second throttle valve having an opening greater than that of the first throttle valve.
In the conventional throttle valve control device, existence of abnormality is determined according to a target position and an actual position of the throttle valve. Both a target opening .alpha. and an actual opening 8 are consequently input as comparable signals into an electronic control unit for executing abnormality detection. This makes the structure of the throttle valve control device undesirably complicated. When a plurality of electronic control units intercommunicate data representing the opening of the throttle valve, abnormality in the actuator can not be discriminated from abnormality in a communication system.
Abnormality in the actuator resulting in abnormal operation of the throttle valve drastically varies the output of the internal combustion engine which gives uncomfortable feeling and uneasiness to a driver. Such abnormality should thus be detected without delay. A relatively long time is, however, required for abnormality detection when data are input through communication. In a structure that a throttle valve is pressed in a fail-safe direction, an electronically controlled throttle includes a spring for pressing the throttle valve in a full-closing direction (in the case of a single throttle valve structure) or in a full-opening direction (in the case of a dual throttle valve structure). When abnormality in a stepping motor working as the actuator reduces a valve sustaining torque, the throttle valve is abruptly driven in the full-closing direction or the full-opening direction. This results in an abrupt change of the air intake in the internal combustion engine. Delay in the abnormality detection may cause abrupt acceleration or deceleration.